There are two heads of biceps femoris- short & long. The long head forms the lateral part of hamstrings.

ORIGIN:

• Short head of biceps femoris originate from lateral lip of linea aspera of femur between the adductor magnus & vastus lateralis, upper two-thirds of lateral supracondylar ridge & lateral intermuscular septum
• Long head of biceps femoris originate from common tendon with semitendinosus from inferomedial impression of the posterior portion of upper part of ischial tuberosity and lower part of sacrotuberous ligament.
The fibres of the long head form fusiform belly and pass obliquely downward & laterally across the sciatic nerve and ends into an aponeurosis. The aponeurosis covers posterior surface of the muscle & blends with the fibres of short head of biceps femoris.

INSERTION:

• The aponeurosis contracts into a tendon which is either folded around or is split by the lateral collateral ligament. It inserts into lateral side of head of fibula infront of its apex or styloid process & lateral collateral ligament. Then it splits into three laminae- the intermediate lamina fuses with lateral collateral ligament & other two pass superficial & deep to the ligament to attach to lateral condyle of tibia.

INNERVATION:

Long head-Tibial part of sciatic nerve (L5, S1, S2) & Short head- common peroneal nerve (L5, S1, S2)
BLOOD SUPPLY: Anastomoses of perforating branches of the profunda femoris artery, inferior gluteal artery and superior muscular branches of popliteal artery

ACTIONS:

• The long and short head of biceps femoris work in sync with each other to perform knee flexion.
• The long head extends the femur at hip joint as it originates in the pelvis.
• The biceps femoris because of its oblique direction laterally rotates leg, when the knee is semi flexed.
• When the hip is extended, the biceps femoris is a lateral rotator of the leg.
Active insufficiency
As long head of biceps femoris is two joint muscle, crossing hip as well as knee joint, it performs movements at both the joints. However it cannot simultaneously contract at both the joints with 100% tension. It is a weaker knee flexor when the hip is extended and a weaker hip extensor when the knee is flexed.

Synergists:

 

• Semitendinosus, Semimembranosus work along with both heads of biceps femoris to perform knee flexion.
• Biceps femoris and Gluteus maximus, Semitendinosus, Semimembranosus, Adductor Magnus (posterior fibers) performs hip extension.

Antagonists:

• Vastus Lateralis, Vastus Medialis, Vastus Intermedius, Rectus Femoris- all four combine and form Quadriceps muscle which produces knee extension.
• Popliteus, Semitendinosus & Semimembranosus are attached on the medial side of knee and thereby internally rotate the leg when knee is flexed, in oppose to lateral rotation torque produced by biceps femoris.
• Psoas Major, Iliacus are chief hip flexors.

Fascial integration:

• The fascia of the leg receives a thin expansion from the posterior border of the tendon.

• The lateral intermuscular septum of the thigh, situated between the vastus lateralis & biceps femoris, is a deep fascia in the thigh- the Fascia Lata. It separates the anterior compartment of the thigh from the posterior compartment of the thigh.

Fascia lata is thicker in the upper and lateral part of the thigh, where it receives a fibrous expansion from the Gluteus maximus, and where the Tensor fascia lata is inserted between its layers. It is very thin behind and at the upper and medial part, where it covers the Adductor muscles, and again becomes stronger around the knee, receiving fibrous expansions from the tendon of the Biceps femoris laterally, from the Sartorius medially, and from the Quadriceps femoris in front.

• The fascia lata is attached in front to the inguinal ligament, above and behind, to the back of the sacrum and coccyx; medially, to the inferior ramus of the pubis, to the inferior ramus and tuberosity of the ischium, and to the lower border of the sacrotuberous ligament, & laterally, to the iliac crest and to the superior ramus of the pubis.

• Laterally, the fascia lata receives the greater part of the tendon of insertion of the Gluteus maximus, and becomes proportionately thickened.

• It passes down over the Gluteus medius from its iliac crest attachment to the upper border of the gluteus maximus where it splits into two layers- one passing superficial to and the other beneath this muscle which unites at the lower border of the muscle and forms a strong band.

• This band continues downward as iliotibial band and is attached to the lateral condyle of the tibia. The deep surface of the fascia lata gives off two strong intermuscular septa.

a. The lateral and stronger one extends from the insertion of the Gluteus maximus to the lateral condyle which separates the Vastus lateralis in front from the short head of the Biceps femoris behind from where these muscles originate.

b. The medial and thinner one separates the Vastus medialis from the Adductors and Pectineus.
c. Besides these there are numerous smaller septa, separating the individual muscles, and enclosing each in a distinct sheath.

Postural dysfunction:

• Human body is a kinetic chain. All body parts including the joints are interconnected. Any malalignment or pathology at one particular joint can alter the alignment at other joint/joints and lead to biomechanical fault. Immense studies have been conducted already on hamstring tightness and various pathologies of back, hip, knee, ankle and even neck. There exists a strong correlation between them.
• Two major & common pathologies occur related to biceps femoris- tightness and strain.

Hamstring Muscle Tightness/Shortening:

• Poor Posture for prolonged period of time causes muscle to undergo tightness. Most common is sitting with sustained knee flexion in office chair or at home. Or any pathology at proximal or distal joints can lead to protective knee flexion for sustained duration or even during prolonged immobilization following fracture or soft tissue injury of lower limb.

• The commonest reason that why majority of times hamstring muscle group undergo tightness is we generally are not using full length of it in our activities of daily living and thereby the unused part undergoes tightness even in normal individuals.

• Tight hamstrings are associated with low back pain and low back pain may cause hamstring tightness. Hamstrings produce hip extension and knee flexion. And tight hamstrings can stop the hips from flexing forward during forward bending and lead to low back pain as lower back will have to bend beyond its strong middle range.

• This alters the lumbo-pelvic rhythm causing the lumbar spine to bend forward more as forward rotation of the pelvis will be restricted resulting into strain and pain. And so stretching the tight hamstrings is considered to be a vital portion in cases of low back pain. If this isn’t treated at proper time there will be altered back and lower limb kinematics and kinetics leading to lower crossed syndrome.

• Lower crossed syndrome is a condition where muscles on one diagonal at a joint become tight and hypertonic whereas on the other diagonal are weak and lengthened.

 

Clinic HQ
• Repetitive overuse of Biceps Femoris, Semimembranosus, Semitendinosus and tight thoraco-lumbar extensors & iliopsoas, weak & lengthened Abdominals, Gluteus Maximus, Gluteus Medius puts stress on Biceps Femoris to remain contracted. Prolonged contraction causes local ischemic changes in the muscle leading to development of fibrous nodules and thereby triggers points.

(Trigger Points)
Hamstring Muscle

 

Referances:

1.  Kinesiology, The mechanics & Pathomechanics of human movements , Carol A.OATIS , Lippincott Williams & Wilkins, Philadelphia
2. The muscular, ligamentous and neural structure of the lumbosacrum and its relationship to low back pain. FH Willard, movement, stability & lumbopelvic pain, 2007.
3. Biceps femoris- Wikipedia
4. Biceps femoris- university of Washington
5. Biceps femoris- thewellnessdigest
6. Myology-bartleby